Sounds like you may have a combination of problems. The shear pin can be a little lose in the shaft (but should be snug) as long as it's tight in the spindle. hence second problem. Sounds like you have too much negative movement and its pushing on the spindle, which would put pressure on the pin causing the oval hole. You may have originally set the swash a tad high causing the difference. You can try a cut off T-pin like they use on posterboard and stuff. You know, they look like straight pins and are shaped like a T on top. These are slightly thicker than the standard shear pin, but work well for an oversized hole. You should probably pick up a main shaft/gear set and spindle, because it sounds like you've got way too big an opening. The reason I suggest the T-pin is if you have to order parts at least you can still fly.